If you do the oven method use parchment paper not waxed. It only takes a few minutes and kind of looks like Shriky Dinks back in the 80s. It'll move around a little and then lay down. Pull it out at that point and put whatever on top. I used a huge old atlas that still had the unified Soviet Union in it and put some extra books on until it cooled off.

If you have long plastics I find they shink enough that you might need to elongate the screw holes a bit to get it back on the posts.

I dug up some information from one of my old posts:1) I started the oven at 200 degrees.

2) After the oven warmed up, I placed the plastic (printed side up) on a piece of parchment paper and both onto a cookie sheet.

3) After 8 minutes and nothing happening I cranked it up to 250 degrees and within 2 minutes I witnessed the plastic starting to flatten out.

4) It took about 10 seconds to flatten so I pulled it out.

5) I placed it with the parchment paper underneath directly on the flat countertop and under a large book until it cooled (10 minutes was fine).

Conclusion: I found 200 degrees wasn't warm enough, but it probably was a good method to bring the plastic's temp up slowly without flash burning the painted side of the plastic. I am quite comfortable with the results and I am not hesitant to carry this method out on the rest of my pieces.

If you use a jug of washer fluid like Ted said get -40C. -42C is some bullshit selling feature. 2C doesn't make a difference and whoever goes about buying the "bug guts pink stuff" is plain nutty. Get the $2.99 jug from the grocery store. Buying those $5.99 jugs at the gas station is highway robbery. There should be a law against that.